Method of heat treating metal shot



Aug. 17, 1965 o. 1 STEWART METHOD OF HEAT TREATING METAL SHOT 4 Sheets-Sheet 1 Filed Jan. 18, 1962 lOl Aug- 17, 1965 o. L. STEWART 3,201,289

METHOD OF HEAT TREATING METAL SHOT Filed Jan. 18, 1962 i 4 Sheets-Sheet 2 FIG. 5 40 f-GO so 62 68" 67 6| FIG. 4

i/.feo "7 el 'md5-mux- INVENTOR.

ORALD L. STEWART BY cyayfczef/ ATTORNEYS Aug. 17, 1965 o. l.. STEWART METHOD OF HEAT TREATING METAL SHOT 4 Sheets-Sheet 5 Filed Jan. 18, 1962 INVENTOR.

ORALD L. STEWART ATTORNEYS Aug. 17, 1965 o. L. STEWART 3,201,289

METHOD OF HEAT TREATING METAL SHOT Filed Jan. 18, 1962 70 nov A.c.

4 Sheets-Sheet 4 o o o o o o HIGH LIMIT OOO O00 o ooo ZONE2 B u zoNE INVENTOR. ORALD L. STEWART United States Patent land Metal Abrasive Co., (leveland, Ohio, a corpora tion of Uhio Fiied dan. 18, 1952, Ser. No. 167,@21 2 Claims. (Cl. 143-131) This invention concerns a heat treating method and apparatus, particularly adapted for use in the heat treating of metal abrasive shot. In its broadest sense, the method comprises the steps of continuously heating and rotating a substantially closed smooth-bore retort, automatically feeding metal particles into said rotating retort adjacent one end thereof until the metal particles arrange themselves into a substantially continuous path over a substantial length of the retort, and finally automatically discharging the metal particles from the retort into a cooling medium on a substantially first-in, rst-out basis.

A novel apparatus combination is provided for performing the heat treating method and includes housing means, heating means for automatic controlof the temperature Within said housing means, retort means extending through said housing means and having a smooth cylindrical bore, cap means at either end of .said bore substantially closing said retort means, drive means imparting rotational movement to said retort means, automatic feed means supplying said retort means with metal particles adjacent one end of the cylindrical bore, and automatic discharge means dispensing said metal particles into a quenching bath from said retort adjacent the other end of said cylindrical bore on a substantially first-in, iirst-out basis.

The furnace of this invention is adapted especially to heat small metal particles to any`temperature up to approximately 2,000 F. on a continuous ow basis at various rates, depending on the temperature. For example, in one form and size it can heat 2,500 pounds of steel shot per hour to a temperature of 1700" F. The furnace of the invention has a multitude of advantages not found in metal abrasive shot heat treating apparatus of the type heretofore known in the shot producing industry, which resultV in low initial cost, low operating cost, and low maintenance cost.

Rotary retort furnaces of the general type herein disclosed are not new. in fact, their use in calcining processes is rather Well known; however, the novelty and advantages of a furnace constructed according to the' principles of this invention and the method of using said furnace in heat treating metal abrasive shot, lies in its` efficient retort design, mechanical drive design, and control set up, all of which cooperate'to make possible a continuous metal shot heat treating process of extreme efliciency which requires a minimum of manual labor and supervision. The known prior art rotary furnaces for heat treating metal have contained ribbed spirals and tion to follow.

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In the prior art methods of heat treating metal abrasive shot it has been necessary conventionally to provide some Y type of positive Work driving or propelling means, such as internal retort flights, vibrating chutes, or batch type baskets trays,` to move the metal abrasive particles into and out of the furnace. The use of these expensive prior art propelling means has result in high replacement and maintenance costs which are attributable` in a large measure to the sticking of the hot metal particles to the propeliing means Within the retort.

The prior art has relied upon Athe use of expensive and complicated controlled atmosphere systems, to minimize the metal abrasive particle sticking Within the retorts, which have been characterized by the provision of elaborate sealing structures and control apparatus. The compact furnace of the instant invention, by eliminating the need for metal abrasive particle propelling means and using a smooth bored retort has eliminated substantial partical sticking and the need for the prior art type of controlled atmosphere and sealing means in heat treating metal abrasive shot and, therefore, has reduced both the manufacturing and maintenance costs of the furnace While increasing the capacity thereof. it is possible, however, that for use in metallurgical processes, such as carburizing and case hardening, the furnace of this invention can be converted easiiy Vfor efficient use with special atmospheres in view of the substantially closed retortmeans utilized.

Gther prior art problems which traditionally have b'ee encountered in rotary retort apparatus are those caused by heat transfer from the retort to the elements in the drive mechanism f'or rotating the retort. Heat transfer to these pats has resultedin high maintenance costs due to the fact that the heat softens and weakens the metal and thereby causes wear and distortion which results in misalignment of wheels, damage to bearings, and fatigue of gear and chain elements. i

The prior art feeding and control apparatus for rotary retort furnaces has been elaborate and inefficient and has not'safeguarded adequately the quality of the products being treated therein.

there has been a constant problem of volume production due to therheat treating necessary to maintain uniform high quality shot. The continuous heat treating furnace i and method provided bythe principles of this invention It is, therefore, the general object of the invention to i provide an improved method and apparatus useful in connection with the continuous `heat treating of metal abrasive shot. i t y It is a more specific object to provide a heat treating method and furnace for metal abrasive shot which auto-V i matically controls, feeds and discharges the shot into a quench bath with a minimum of human attention and a maximum of high quality uniformity.

Other and more specific objects of the invention 'will be apparent from the drawings and the detailed descripln the drawings:

FIG. 1 is a side elevation View withcertain of the .parts` With the increased demands of industry for high qualityinetalabrasive shot material,`

FIG. 2 is an elevation view of the input end of the furnace of FIG. 1;

FIG. 3 is a cross-ssectional view of the furnace along the line 3 3 of FIG. l;

FIG. 4 is an elevation view of the discharge end of the furnace;

FIG. 5 is a schematic side elevation View showing the furnace burners and controls;

FIG. 6 is a wiring diagram of the furnace control means.

The specific furnace and method embodiments shown and described utilize a two-zone heat control system for the furnace combination; however, single or multiple zone versions are contemplated. A single zone type of heat control has been found to be successful but is slightly less eflicient than the described two-zone system.

Referring now more particularly to the drawings, the apparatus of this invention comprises a furnace combination 10 which includes housing means 20, heating means 30, retort means 4t), feed means 50, retort drive means 60, electrical control means '70 (see FlG. 6), quenching means 80, conveyor means 90, and power transmission means 100.

As seen in FIGS. 1 and 3 of the drawings, the housing means of the illustrated furnace combination l@ is an elongated trough-shaped metal casing 21 lined by a refractory brick structure 22. having a central cavity 23 ywhich is of a semi-circular cross-sectional shape in its lower portion 24 and is of an enlarged irregular shape in its upper portion 25 adjacent the heating means 30. The retort means 40 extends through openings 26 and 27 in the ends of housing means 20 and is supported externally for rotation therein about the axis of the semi-circular lower portion 24 to provide for the ecient distribution of heat within the cavity 23. Venting passageways 23 are disposed in the upper portion of the cavity 23 to permit removal of the combustion gases generated during operation of the furnace.

The heating means includes conventional air-gas burners 35, such as the type produced and sold by North American Manufacturing Company of 4455 East 71st Street, Cleveland 5, Ohio, under the designation of Series 4423-3B. These burners include an observation port and combustion tile and are equipped with pilot tips for lighting. The burners are mounted in openings 29 in housing means 20 and are capable of close regulation by varying automatically the air-gas supply thereto in a manner hereinafter to be described. Several different nurnbers of burners, preferably from 4 to l2, may be used in V the furnace depending on the temperature requirements of the desired heat treating process.

For example, in the embodiment described herein a bank of six burners has been found to be satisfactory for a wide range of applications. When operated together with an air pressure of 8 p.s.i., these six burners are capable of producing 1,830,000 B.t.u. per hour from a 2O inch llame.

In geographic areas Where electrical power rates are low, electrical heating means for the furnace could be substituted for the gas means described, or, as will b-e obvious further to those skilled in the combustion art, a suitable oil combustion system also could be used if desired.

The retort means of the furnace 10'is a generally cylindrical metal casting or fabrication, 41, of greater length than the housing means 20 having a smooth central bore 4Z therein. Cylinder 41 has an apertured radially inwardly directed ange 4in welded or otherwise providedA at each end thereof for connection of the end structure thereto. SuitableV fastening means, such as bolts 41b extend outwardly through ange 41a to secure apertured radially outwardly directed tire-like circular flanges 45 and 46 to the ends of cylinder 41. The anges or tires 45 and V46 are retained in place on bolts 41h, concentric with cylinder 41, by suitably apertured and centrally bored end caps 43 and 44 and nuts 41C threadedly associated on the k alloy steel.

bolts extending through the aligned apertures of the members. Rotational motion is imparted to the retort by frictional drive on the outer surfaces of the tires 45 and 4d in a manner to be explained later.

The described fastening arrangement for the end structure of cylinder 41 is preferred, although other fastening means may be used in the combination because of the convenience of assembly and disassembly which it affords. It has been found in this respect that by mounting the bolts 4111 close to the bore 4, as illustrated in FIG.V 1, the tool pads on the bolt heads prevent rotation of the bolts relative to the apertured members, and the nuts, therefore, may be threaded or unthreaded without having to hold the bolts with a wrench or other means on the inside of the structure. A series of holes 49 opening radially through the wall of the retort cylinder 41 are spaced symmetrically around the periphery thereof adjacent the discharge end of the furnace outside of the housing means Ztl for substantially continuous discharge of shot from the rotating retort.

An automatic feed valve Si? for introducing metal shot particles into the bore 42 of the retort 10 is connected to be responsive to the furnace when it is operating. The valve 50 is mounted adjacent a funnel 51 and when the valve 5t) is open shot flows into the funnel and through a passageway 52 connected thereto, past the hole 48 of the end cap 43, into the retort bore 42. The particles then flow along the rotating smooth bore 4Z in a manner analogous to the iiow of a liquid until they are discharged on a rst-in, first-out basis through the ports 49 into a quenching or cooling medium.

The retort cylinder 41, which is produced either by casting or fabricating, is preferably of heat-resistant high- The uniform cross section of the retort wall and the smooth bore 42 provide a uniform cross section which prevents excessive thermal stresses from building up as the temperature of the retort changes. These stresses, if not reduced in this manner, would cause rapid fatigue of the retort and eventual cracking. This provision greatly prolongs the life of the retort cylinder.

Another particular advantage of the retort is that the smooth finish of bore 42 minimizes sticking of heated metal particles to the inside surface. This significantly increases the operating time between retort cylinder cleanings and renders the use of controlled atmosphere in the furnace unnecessary, thus greatly reducing cost. This sticking problem with retorts for heating metal particles is a critical one because materials sticking to the inside of the retort results in poor heat transfer and consequently reduction in production. This is caused by the formation of a ring of metal from the shot particles with a different expansion rate than the retort itself, thus setting up higher stresses. The reason that the smooth bore type of retort can be used for heat treating shot is that the small metal particles behave as a liquid when agitated by the rotating motion of the retort. This action causes the particles to travel uniformly through the retort in a continuous iiow as new material is introduced on the feed end to displace material out of the discharge end outlct on a substantially first-in, first-out basis. Of course, the retort cylinder can be used in other than a horizontal position because of this 'action and it is possible to give the structure a slight tilt in either direction, but in order to avoid bearing overloading in the drive mechanism or misaligning the driving parts, the horizontal position is preferred.

According to the feed principles used in the furnace of this invenion, a rotational motion must be imparted to the retort to effect uniform heating of the retort and to keep the metal particles progressing through the furnace. ln-l the disclosed embodiment of the invention, a rotation rate k of 7 to 10 revolutions per minute has been found opti-- mum; however, this may vary widely depending upon the particular heat treating procedure being used. The par-- ticular described shape of the cavity 23 ef the housing:

means Ztl is designed for optimum distribution of heat in the furnace and creates a circulation of air around the retort as shown by the arrows in FIG. 3.

The retort drive means t@ includes two longitudinal shafts 6l and 62 mounted in pillow blocks at either end axially outwardly from the retort tires 45 and 46. Adjacent the pillow blocks on the feed end of the furnace are two flanged wheels d5 and sie conventionally secured on the shafts to rotate therewith. The flanges and wheel Width are such that the tire 45 frictionally engages the inner surfaces of the flanged wheels 65 and 66 between the flanges. Similarly positioned on the opposite ends of the shafts 6l and 62 inside the pillow blocks, in alignment and supporting frictional engagement with the tire 4a are two unilanged wheels 67 and 68. This arrangement provides constant alignment of the retort tire 45 with respect to the flanged wheels 65 and 66 and permits thermal eX- pansion of the retort to be taken up by the untlanged wheels 67 and 6d.

The wheels 65, ed, e7, and 68 are of rather massive construction with a radius determined by the heat transfer characteristics of the material from which they are made, since it is imperative that a minimum of heat be transferred to the shafts 6l and 62 and, of course, to the bearings of pillow blocks e3. Moreover, the tires 45 and 46 of the retort means 40 are large enough so that heat does not travel easily to wheels 65, 65, 67, and 68. This keeps the temperature on the tire peripheries low and results in longer life of both the tires and wheels. Also of importance to the life of the furnace isthe fact that shafts 63 and 64 are provided the full length of the furnace so that misalignment of the wheels which would cause rapid wear is eliminated. Moreover, the frictional drive utilized eliminates the use of low speed-high torque gears or sprockets on the retort cylinder itself and exposure of the drive means to heat which would result in high maintenance costs.

The shaft 6l and wheels en and 53 of the retort drive means dll are driven in any conventional manner by generally designated power transmission means 160, illustrated in FIGS. l and 2 as electric gear motor lill, having a driving sprocket M92 mounted on the shaft thereof and connected by means of chain 1533 to a driven sprocket 104 rigidly mounted on shaft ell by means of key M35.

The means of driving shaft all may be varied, of course,

as by direct gearing, or by a shaft mounted gear head driven by a standard speed electric motor, if desired, and the illustrated power transmission means is provided merely as an example of one practical form which power transmission means ilu@ may take.

The shafts 62 and the wheels 65 and 67 mounted thereon are idlers which receive their rotation from frictions engagement with the rotating retort tires and 46 and, therefore, need not be driven directly by power transmission means lull in the manner in which shaft 6l and Wheels 66 and 68 are driven. The idling shaft 6?. does serve a function in addition to supplying support for the rotating retort cylinder 4l, however, in that a motion sensitive zero speed switch 76 is connected thereto which, if the retort stops rotating for any reason, actuates an alarm 7S, as will be seen in FIG. 6.

As the power means lll@ drives the shaft 61 and retort cylinder 4l and the automatic feed valve Stb is actuated, the metal particles flow through the rotating retort cylinder 41 and are discharged through the ports 49, as previously explained, into a quenching bath St) positioned below the ports. The quenching bath for most metal abrasive shot is a Water bath, but may, of course, by any conventional quenching medium, such as oil or the like, depending on the structure required. Also disposed in the quenching bath container till is a conventional means 99, preferably with dip buckets thereon which cooperate with a sloped floor d2 of the bath container 8l to pick up the shot from the bottom of the bath Sd and remove it to a cool dryer or storage position. Thus, the furnace is set up to heat treat and quench metal abrasive shot without the attention of a full time attendant.

A control means 7ll is provided which alerts responsible persons in the plant to any abnormal condition in the apparatus and an alarm sounds if any of the following things occur:

lf the temperature drops below a desired low limit as indicated by the various thermocouples 7l, such as the one projecting into the retort cylinder 4l through the bore 47 of the end cap 44.

If the furnace temperature rises a predetermined amount above the operating range;

lf the retort stops rotating;

lf the fuel or air supply fails.

rl`he feed valve Sil preferably is a pneumatically operated type clipper valve connected in the control circuit 7@ such that when the first of the aforementioned abnormal conditions occur, the feed of the metal particles to the furnace is stopped. This helps to insure the product is not produced when the furnace is not operating correctly. The pneumatic-ally operated dipper' valve Sti controls the feed rate into the furnace accurately by means of a manually movable stop which limits the opening of the feed gate.

FlGS. 5 and 6 relate to the combustion and control systems of the described furnace and are set forth herein only by way of an example of one practical embodiment of the heating means 3%' -an-d the control means 'lll which may be used in connection with the invention.

The gas combustion system 39 schematically illustrated in FIG. 5 is divided into two zones for accurate temperature control within the furnace. The rst zone is the preheat zone and the second zone is the maximum temperature zone. The first zone includes the three burners to the left or feed end of the furnace and the second zone includes the three burners to the right or discharge end of the furnace.

The gas supply line 3l has connected therein a manually actuable main gas cock Ztll with a limit switch connected in contuol circuit 7u which shuts olf and opens the supply of gas to the furnace. A gas pressure regulator 262 of the conventional diaphragm type keeps the gas pressure to the furnace constant as the main line pressure varies from seasonal or other causes. A safety shut-olf valve 263 is connected electrically in the control circuit 70 to shut :off the gas supply from line 3l when the power fails; the gas pressure drops too low to give proper combustion; the air supply fails; or, the furnace overheats. The valve 293 also may be used to keep the gas olf until all the burner gas cocks are closed for individual opening and lighting. Its connection in the `system will be readily apparent from the drawings and the description to follow.

A low gas pressure switch 2li4 actuates the safety shutoff valve 2%3 through the circuit 7l? if the gas pressure from the gas supply line 3l drops too low. A control of the air-gas ratio is provided by a conventional diaphragh regulator mechanism 203 connected between gas supply line 3l and air supply line 32 and this control assures that a proper gas-air ratio is provided to all of the burners as the air pressure is changed in the line 32.

The zone one burners are normally on high fire at all times during operation of the furnace and a solenoid gas valve 2% connected in circuit 7tl is provided in the zone one branch 33 of gas supply line 31, to control the flow of gas to the zone one burners. If the control circuit 76B registers an excess :of heat in zone one, the solenoid valve 2% `shuts off and the low lire bypass valve 2tl7 provides a restricted gas supply to the burners. The magnitude of the zone one low lire gas supply is such that it is preset by the valve 2537 to a level which is combined with the line 33 gas flow to give the proper high re gas supply during normal operation. The gas pressure gauge Ztl@ is used to check the pressure in line 3.3. A similar gas pressure gauge 2% is mounted inthe zone two branch 34 of the gas supply line 3l. Where closer control is de- `temperature within the zone.

sired, zone one is provided with a ratio control system the same as in zone two.

. The burners 35 of the combustion system 3@ are separated from their respective branch gas supply lines by conventional manually operable safety gas valves 299 which are interconntcted by check line 36 through safety air passages which must be opened Ibefore the safety valve 203 can be opened. To assure that all of the valves 239 are closed, a checking air pressure switch Zitti is connected in the line 3d which prevents the operation of valve 2% until the valves 26E@ have been closed. Also provided between the branch zone supply lines 33 and 34 and the burners 35 are limiting orifice gas valves 2111 for adjusting the flow of gas to each individual burner.

The pilot system for the 'burners 35 is supplied 'by a gas line 37 connected to the main gas line 3l. The line 37 has therein a conventional atmospheric type pressure regulator 213 and a manually operable on-off valve 214 for simultaneously shutting ott and opening the gas line Vto all the pilots. A pilot air supply line 33 is connected in the main air supply line 32 and is connected with the line 37 to a pilot mixer 215 which mixes the gas and air for all the pilot tips 216. The gas-air mixture is conducted through pilot supply line 59 to the individu-al pilot tips 216. The gas burners 35 have observation ports 23.7 located thereon to facilitate their adjustment to the proper flame level.

The airpressure for the combustion system is supplied to the main air supply line 32 Iby a conventional combustion air blower 218. The air supply to the zone two portion of line 32 is regulated by a power operated butterfly air valve which is controlled by the circuit 70 to be opened at any of three positions depending on the rThe air pressure within the zone may be observed by means of a conventional gauge or manometer 22E.

The air supply to the individual burners 35 is adjusted manually by buttery air valves 22?. in the lines between the main air supply line 32 and the burners 35. If the lair pressure gets too low for safe operation, an air pressure switch 223 connected in the control circuit 7i) shuts off the gas safety valve 263. FIG. 6 is a circuit diagram schematically showing the wiring of the 110 volt control circuit 76* which actuates the various mechanisms of the combustion system described in connection with FIG. 5. The power circuit which supplies the current for the motor Miti, the blower 218, and the conveyor 9d is conventional and is not illustrated.

The control circuit 7i) is provided with automatic alarm 75 which may be set by switch 77 to sound olf whenever any of the abnormal conditions previously listed occur.

In addition, indicator lights 7S are provided to show the condition of the key control system elements at any given time. They are used also as a means of determining the source of abnormal conditions.

A switch 201s is provided on manually operable main gas valve 261 to indicate the open-shut position of the valve by means of a light 7 3 in the control circuit 70. A main electrical switch 74 is provided in the circuit 7@ to shut off the power to the remainder of the control circuit.

With the switch 74 closed the control circuit acts such that the pressure switches 2614 and 21th are closed as long vas proper pressures through them are maintained as explained in connection with FIG. 5. Also normally open safety valve relay 203;-, underheat relay 3dr, and retort stopped relay 4th', are connected in the alarm circuit such that if any of the thermocouples 7l indicate an abnormal temperature condition through conventional controllers A and C (such as sold by Minneapolis-Honeywell Regulator Co., Penn and Bay Streets, Fall River, Mass., under the designation Pyr-O-Vane models 105 Y and 106), or the zero speed switch indicates that rotation of the retort has stopped, the alarm is sounded, and de- CIK pending on the nature of the trouble, the safety shutoi valve may be closed. Further provision in the circuit by means of feed switch 79 in connection with the electropneumatic feed vaive Si? automatically shuts ot feed of shot'to the furnace in the event of an abnormal condition.

The two zone control system of the illustrated embodiment is provided such that the gas supply to the zone one burners is controlled by valves 206 and 2637. lf the thermocouple 7ll in zone one, connected in circuit 7@ by means of conventional control and amplifying means A, senses that the temperature within the zone is below 1300 F., the solenoid gas valve 2625 is opened and the burners in the zone are placed on high lire. If the temperature in zone one exceeds G F., the solenoid closes the valve 2% and the low fire bypass which has been preset by gas 207 is the sole supply of gas for these burners until the temperature drops below 1300" F., and the valve 296 again opens. The burners can be adjusted so that this zone levels oif at about 1295o F. and remains on high tire.

The air supply valve 219 to zone two is actuated similarly by a thermocouple connected by means of conventional control and amplifying means B (such as sold by Minneapolis-Honeywell Regulator Co., Brown instruments Division, Philadelphia, Pa., under the designation ElectroniK 17 Controller) in circuit "iti such that by means of the air-gas ratio control means 7,@5, the air is kept in constant ratio to the gas supply and the valve 219 is wide open at 1690 F.; at 1695" F. valve 239 is approximately two-thirds open; at 1700 F., valve 219 is one-eighth open. If the temperature in zone two is below 1680 F., the control 4circuit 7@ insures that the feed is shut oif at the feed valve 5u. A high limit thermocouple 71 has a high limit safety shut-down control and amplifying means C which shuts oit the safety shut-off valve 203 in the event the temperature exceeds 1950 F. in the furnace.

v Accordingly, the method of heat treating metal abrasive shot according to the principles of this invention begins with bringing the furnace up to temperatures so that the controls of circuit 7i) will maintain the temperature automatically. As the metal particles are fed automatically through the feed valve Sti and arrangedV themselves into substantially continuous paths over a substantial length of the rotating retort, a discharging of the metal particles from the ports 49 into the quenching bath 30 occurs on a substantially first-in, rst-out basis. The conveyor 9i? removes the heat treated metal shot from the bath Sti to complete the operation.

For ease of description, the principles of the invention have been set forth in connection with but a single illustrated embodiment thereof. It is not my intention, however, that the illustrated embodiment nor the terminology employed in describing it, be limiting inasmuch as variations rnay be made without departing from the spirit of the invention. Rather, I desire to be restricted only by the scope of the appended claims.

The invention claimed is:

1. A method of heat treating metal shot of substantially spherical shape above a critical temperature comprising f substantially continuously dropping said shot to a rst location adjacent one end of an elongated internally smooth metal supporting structure, continuously rotating said structure thereby to obtain uniform particle heating and to move said shot fromV said first location to a second location adjacent the end opposite said one end and simultaneously to move substantially all of said shot rotationally about the individual shot particle centers, continuously heating the exterior of said structure si- Vmultaneously to conduct heat directly to the shot in direct contact with said structure and to radiate sadness;

heat uniformly to the shot moving between said Irst and second locations, sensing the temperature Within said structure, adjusting the heat applied to the exterior of the structure in response to the temperature sensed within said structure to a desired range of temperature therein, dropping said shot substantially directly from said second location Where the shot is above the critical shot temperature into a desired cooling medium. 2. The method of claim 1 in which the step of dropping said shot substantially directly from said second location into a cooling medium includes the step of immersing the shot in a liquid.

References Cited by the Examiner UNITED STATES PATENTS Pavitt 148-126 X Hall 148-426 X Wick et al. 148-153 Freeman 75-3 Wilson et al.

Delapena et al. 266-4 Eisenmenger 266-4 DAVID L. RECK, Primary Examiner. MORRIS O. WOLK, Examiner. 

1. A METHOD OF HEAT TREATING SHOT OF SUBSTANTIALLY SPHERICAL SHAPE ABOVE A CRITICAL TEMPERATURE COMPRISING SUBSTANTIALLY CONTINUOUSLY DROPPING SAID SHOT TO A FIRST LOCATION ADJACENT ONE END OF AN ELONGATED INTERNALLY SMOOTH METAL SUPPORTING STRUCTURE, CONTINUOUSLY ROTATING SAID STRUCTURE THEREBY TO OBTAIN UNIFORM PARTICLE AND HEATING AND TO MOVE SAID SHOT FROM SAID FIRST LOCATION TO A SECOND LOCATION ADJACENT THE END OPPOSITE SAID ONE END AND SIMULTANEOUSLY TO MOVE SUBSTANTIALLY ALL OF SAID SHOT ROTATIONALLY ABOUT THE INDIVIDUAL SHOT PARTICLE CENTERS, CONTINUOUSLY HEATING THE EXTERIOR OF SAID STRUCTURE SIMULTANEOUSLY TO CONDUCT HEAT DIRECTLY TO THE SHOT IN DIRECT CONTACT WITH SAID STRUCTURE AND TO RADIATE HEAT UNIFORMLY TO THE SHOT MOVING BETWEEN SAID FIRST AND SECOND LOCATIONS, SENSING THE TEMPERATURE WITHIN SAID STRUCTURE, ADJUSTING THE HEAT APPLIED TO THE EXTERIOR OF THE STRUCTURE IN RESPONSE TO THE TEMPERATURE SENSED WITHIN SAID STRUCTURE TO A DESIRED RANGE OF TEMPERATURE THEREIN, DROPING SAID SHOT SUBSTANTIALLY DIRECTLY FROM SAID SECOND LOCATION WHERE THE SHOT IS ABOVE THE CRITICAL SHOT TEMPERATURE INTO A DESIRED COOLING MEDIUM. 